In the case of a natural radiating environment, one effect against which the invention provides protection is called a singular effect. This is a non-destructive effect which takes the form of a reversal of one or more pieces of logic information stored in an electronic memory. Effects of this kind are prompted by the input of electrical charges following the passage of an ionizing particle, whether directly or indirectly.
There are a certain number of error-detection and error-correction techniques existing at present that are implemented to address this set of problems. However, their efficiency is proportionate to their complexity and cost. This is why any use is often restricted to the most vitally important elements of a system. The unit information element, known as a bit, is a piece of binary information and can take the value “1” or “0”. A set of several bits is called a word. The criteria determining the efficiency of an error-detection and error-correction technique are the number of erroneous bits that can be detected in a word, the number of erroneous bits that can be corrected, the processing time and the quantity of resources needed to make these detections and corrections. The rate “R” is the ratio between the number of bits to be corrected and the number of bits to be stored.
In order of complexity, several different detection and correction techniques can be distinguished. The parity codes technique enables the detection of only one error in a word. For a piece of information encoded on N bits, an additional bit is stored. This technique does not enable error correction. The Hamming codes technique can be used to detect two errors and correct one error in a word. The Hamming code (11, 7) for example thus makes it possible to correct a 7-bit piece of information by adding 4 additional bits. This code is the one whose rate, i.e. the number of bits transmitted relative to the number of payload bits, is the maximum in the context of the correction of a single bit in a word.
The Reed-Solomon codes technique corrects several errors within a same word. For an N-bit piece of information and to correct K bits, it is necessary to store N+2K bits. Thus, to correct the totality of the N bits of the word, it is necessary to store 3×N bits. The rate is therefore R=⅓.
The triplication technique uses triple redundancy, i.e. each piece of data is stored in three copies. A voter-type element compares the three pieces of data and selects the value that appears at least twice. As in the previous techniques, to protect the N bits of a word, 3×N bits have to be stored. The rate is therefore also R=⅓.
At present, systems that protect the totality of the bits of a word therefore need to be able to store at least three times more information, giving a rate R=⅓. The proposed invention is a technique for detecting and correcting the totality of the bits of a word, whatever its length, and therefore calls for less storage of additional bits than do existing techniques, the rate being closer to R=½.